Can you find out the missing number in the grid?

A non-stop marathon is the shared favourite sport of three brothers.

*The oldest one is fat and short and trudges slowly on.
*The middle brother's tall and slim and keeps a steady pace.
*The youngest runs just like the wind, speeding through the race.

"He is young in years, we let him run!" the other two brothers explained, "'because though he is surely number one, he is second, in a way." Why is it?

What happened when the wheel was invented?

Find the next number in the sequence

5 12 24 36 ?

Solve the rebus riddle in the picture below.

I am the beginning of the end, and the end of time and space. I am essential to creation, and I surround every place. What am I?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

Give it food and it will live; give it water and it will die.

A frog is at the bottom of a 30-meter well. Each day he summons enough energy for one 3-meter leap up the well. Exhausted, he then hangs there for the rest of the day. At night, while he is asleep, he slips 2 meters backwards. How many days does it take him to escape from the well?

It's a test that will check your IQ.

Suppose you have one 11 minute hourglass and one 13 minute hourglass.

Can you measure exactly fifteen minutes using them ?